Field of the Invention
The present invention relates to a sheet feeding apparatus which separates and feeds the sheets stacked on the sheet stacking portion one by one to convey the sheets to an image reading portion or an image forming portion, a sheet reading apparatus with the sheet feeding apparatus, and an image forming apparatus with the sheet feeding apparatus.
Description of the Related Art
For example, in an image reading apparatus in which plural sheets of originals are placed on an original stacking portion and these originals are separated and fed one by one to be read, the originals stacked on the original stacking portion are fed from the stacking position to the separating portion disposed downstream in the original conveying direction by a pick-up roller. A guide surface which extends from the original stacking portion to the separating portion is inclined so that the tip of an original is smoothly introduced to the separating portion.
The pick-up roller abuts on the uppermost original sheet of a bundle of originals when the uppermost original sheet is fed from the bundle of originals. In such a case, especially when a thin original sheet is fed, not only the uppermost sheet on which the pick-up roller abuts but also the sheets under the uppermost sheet are fed at the same time due to friction resistance between sheets. Thus, the tips of plural original sheets arrive at the separating portion from the stacking position.
In the system in which a separating pad is used, the separating pad abuts on a feed roller to form a separation nip in the separating portion. In the system in which a retard roller is used, the retard roller which rotates in the direction in which a sheet is returned abuts on the feed roller to form a separation nip in the separating portion. When plural originals are fed by the pick-up roller, the first original on which the feed roller abuts is fed but the second and subsequent originals under the first original are dammed by the separating pad or the retard roller so that only one original is fed (Japanese Patent Application Publication 2000-62989).
As explained above, when plural original sheets are fed to the separating portion, originals subsequent to the first original are dammed at the separation nip. However, after the tips of the subsequent originals are dammed by the separation nip, the feed of original sheets is performed in a certain amount and a conveying force is continuously applied to the sheets dammed at the separation nip by the pick-up roller. Thus, a thin original sheet having low stiffness is buckled, causing a conveyance failure.